It is known [J. Chem. Soc. pages 470 to 476 (1962)] that 17-iodo-androsta-5,16-dien-3.beta.-ol is obtained by reacting the 17-hydrazone derivative of dehydroepiandrosterone with elemental iodine in the presence of triethylamine in tetrahydrofuran. By using pregnenolone-20-hydrazone as starting material, under similar reaction conditions 20-iodopregna-5,20-dien-3.beta.-ol can be prepared.
The further development of the above process by investigating the role of base and water is discussed in another literature reference [Tetrahedron Letters 24, pages 1605 to 1608 (1983)]. According to this publication the 17-hydrazone of dehydroepiandrosterone is similarly used as starting material, but tetramethylguanidine is employed as base. The transformation of non-steroid hydrazone derivatives is also exemplified.
The reaction of hydrazone derivatives with N-bromo-or N-chlorosuccinimide is discussed in a publication [Chem. Pharm. Bull. Japan 11, pages 1413 to 1417 (1963)]; according to this the 17-hydrazone derivative of epiandrosterone is used as starting material, which is reacted with N-bromo- or N-chlorosuccinimide. This reaction becomes complete within a few minutes, which can be observed on cessation of the evolution of nitrogen. After pouring onto water the reaction mixture is extracted and then the "vinyl halide-type" compounds formed are purified by chromatography or recrystallization.
A similar method is published also in the Hungarian patent No. 171,166. In this process the hydrazone of androst-2-en-17-one is reacted with an N-halogenosuccinimide in pyridine at a temperature between -30.degree. C. and +20.degree. C. to obtain the "vinyl halide-type" final product.